Flexible compression device and coolant circuit therewith and method therefor

Abstract

The invention relates to a compression device (1) comprising a plurality of single-flow compressors (47, 47a) or a multi-flow compressor (3) with a plurality of delivery flows (9, 9a, 9b), wherein the delivery flows (9, 9a, 9b) or the single-flow compressors (47, 47a) are designed such that they are operable in parallel to compress a refrigerant from a lower pressure to a higher pressure, wherein one or more of the delivery flows (9, 9a, 9b) or single-flow compressors (47, 47a) are designed such that they can be switched over in such a way that they can be operated, in a switching setting, to compress the refrigerant of a first partial flow from an average pressure lying between the lower pressure and the higher pressure to the higher pressure, wherein at the same time the remaining one(s) of the delivery flows (9, 9a, 9b) or single-flow compressors (47, 47a) is / are operable to compress the refrigerant of a second partial flow from the lower pressure to the higher pressure,and that the compression device (1) has at least one switching device (5) with one or more shuttle valves provided for switching the switchable one or more delivery flows (9, 9a, 9b) or single-flow compressor (47, 47a). Furthermore, the invention relates to a refrigerant circuit (23) with an economizer (27) and such a compression device (1), as well as a method therefor.

Description

Field of technology:

[0001] The invention relates to a compression device according to the preamble of claim 1. The compression device comprises a plurality of single-flow compressors or a multi-flow compressor with a plurality of discharge flows, wherein the discharge flows or the single-flow compressors are configured such that they can be operated in parallel to compress a refrigerant from a lower pressure to a higher pressure. Such compression devices are used in particular in refrigeration systems, air conditioning systems, or heat pumps for compressing a refrigerant in a refrigerant circuit relating to the invention. In addition to the at least one compression device, the refrigerant circuit comprises, connected in the circuit to refrigerant lines, at least one heat exchanger operable as a gas cooler / condenser, at least one expansion element, an economizer, and at least one heat exchanger operable as an evaporator.

[0002] The warm refrigerant compressed during operation in the compression device has its heat extracted in at least one gas cooler / condenser and then expanded in at least one expansion device, where it cools down. After flowing through at least one evaporator, particularly during normal operation, the evaporated refrigerant finally returns to the compression device for further compression.

[0003] Furthermore, the invention relates to a method for operating such a refrigerant circuit.

[0004] An economizer can be used to increase the COP of a cycle, depending on operating conditions. In a secondary branch of the refrigerant circuit, the refrigerant previously compressed in the compression unit is expanded to a medium pressure, where it cools down to extract heat from the compressed, warmer refrigerant in the economizer, thereby increasing the cycle's performance. The greater the temperature difference between the heat sink at the condenser / gas cooler and the heat source at the evaporator, the greater the improvement in the COP achieved by an economizer. However, if this temperature difference is too small, the available heat transfer surface of the economizer is too small for the economizer to operate economically.

[0005] There are designs of refrigerant circuits in which the refrigerant is operated supercritically on the high-pressure side, such as with CO2 as the refrigerant, and other designs in which the refrigerant is operated subcritically on the high-pressure side, such as with R1234yf as the refrigerant. State of the art:

[0006] Compression devices with multiple parallel-connected single-flow compressors or with multiple parallel-connected discharge flows of a multi-flow compressor are known. US2009 / 0175748 A1 discloses compression devices with multiple compression stages, wherein two compressor subunits are connected in parallel, but the refrigerant compressions in the two compressor subunits have different pressure differences. In the refrigerant circuits disclosed in US2009 / 0175748 A1, one or more secondary branches exist for one or more economizers, wherein the respective suction gas inlet of a respective discharge flow is permanently assigned for the portion of the refrigerant flow of the respective secondary branch or the main refrigerant branch, resulting in a lack of flexibility in the operation of the compression device in the refrigerant circuit.

[0007] DE10354719 A1 discloses a conveying device, for example, as a compressor for compressing a medium, in which two conveying units are switchable in series as a multi-stage or in parallel as a multi-flow, i.e., two conveying flows. These two switching options have the disadvantage of a significant difference in the size of the volume flow to be compressed.

[0008] US2009 / 0320506 A1 shows a refrigerant circuit with a secondary branch with an economizer that can be switched off for the refrigerant passage, but the compression device does not disclose a parallel connection of conveying flows, but only a two-stage arrangement with an additional suction gas inlet for the part of the refrigerant from the secondary branch with medium pressure after the economizer.

[0009] CN108759157 A and US2017 / 0159977 A1 each disclose a refrigerant circuit with an economizer and a two-stage compression device, in which multiple compressors are arranged in parallel in both the low-pressure stage and the high-pressure stage. Connected in parallel, the compressors of the low-pressure stage compress the refrigerant from a low pressure to a medium pressure, and connected in parallel, the compressors of the high-pressure stage compress the refrigerant from a medium pressure to a higher pressure. Multiple compressors are provided in each compression device for both the low-pressure stage and the high-pressure stage, which requires increased material and space.

[0010] In CN108759157 A, the pressure differences between the parallel-connected compressors in a stage are always the same. This limits the flexibility of the compression device disclosed in CN108759157 A. In US2017 / 0159977 A1, however, a parallel-connected compressor in the high-pressure stage of the compression device can be switched over in such a way that it can compress with a different pressure difference than the other parallel-connected compressors in the high-pressure stage. However, this switchable compressor can only compress the refrigerant from the medium pressure of the secondary branch running through the medium-pressure side of the economizer. Compression in the high-pressure stage from a lower pressure can only occur in the other parallel-connected compressors in the high-pressure stage. This limits flexibility.DE69722146 T2 discloses a refrigerant circuit with an economizer and a compression device with capacity control. The compression device includes two connectable parallel low-pressure stages and a common high-pressure stage. Thus, the compression device has two compression stages, making it quite complex and difficult to control. DE102005009173 A1 discloses a refrigeration system comprising a refrigerant circuit with at least two parallel compressors, each having an additional compressor stage that can be used selectively to compress refrigerant from the main mass flow or to compress refrigerant from the additional mass flow. The switching of the operating modes is controlled by a controller using controllable switching valves.These compressors therefore have two compression stages, which makes them quite complex, and switching between operating modes must be actively controlled with controllable switching valves. DE112017005948 T5 discloses a refrigerant circuit without an economizer and with a compression unit comprising at least two compressors connected in parallel. In heat pump operation, the individual compressors can be switched between compressing refrigerant from a low-pressure level to a high-pressure level or from a medium-pressure level to a high-pressure level using controllable switching valves. This requires active control of the switching valves.In the refrigeration machine disclosed in DE102014113167 A1, one of the two parallel compressors of the compression unit can only be actively switched between compressing refrigerant from a low-pressure level to a high-pressure level or from a medium-pressure level to the high-pressure level with a control unit using a switchable three-way switching valve. This switches between operation with or without an economizer.

[0011] The invention defined in claim 1 is therefore based on the problem that switching devices for switching operating modes of previous compression devices with multiple single-flow compressors or one multi-flow compressor are in need of improvement. Furthermore, the savings in space and material and / or components to be controlled of previous compression devices of this type are in need of improvement.

[0012] The object is therefore to provide an improved compression device with several single-flow compressors or with a multi-flow compressor.

[0013] A corresponding task exists for a refrigerant circuit with an economizer and with such a compression device.

[0014] Furthermore, it is a further object to provide a method for operating a refrigerant circuit with a switching device of the compression device for switching between operation with or without an economizer. Summary of the invention:

[0015] The problem underlying the invention defined in claim 1 is solved by the features set out in claim 1. In that a compression device comprises a plurality of single-flow compressors or a multi-flow compressor with a plurality of discharge flows, wherein the discharge flows or the single-flow compressors are configured in such a way that they are operable in parallel to compress a refrigerant from a lower pressure to a higher pressure, and wherein one or more of the plurality of discharge flows or single-flow compressors are configured to be switchable such that, in a switching setting, it / they are operable to compress the refrigerant of a first partial flow from an intermediate pressure lying between the lower pressure and the higher pressure to the higher pressure,wherein at the same time the remaining one(s) of the plurality of discharge flow or single-flow compressors is / are operable to compress the refrigerant of a second partial flow from the lower pressure to the higher pressure, and the compression device has at least one switching device configured such that it comprises one or more shuttle valves and is provided for switching the switchable one or more discharge flow or single-flow compressors, the problem is solved.

[0016] A compression device is a conveying device designed to compress a medium. Conveying flutes, for example, are the conveying units of a multi-fluid compressor with multiple conveying units.

[0017] A shuttle valve typically has two inlets. Depending on the pressure at the inlets, the flow of medium, in this case refrigerant, is automatically controlled from one or the other inlet.

[0018] The switching device comprises a shuttle valve even if it is designed as only a single shuttle valve.

[0019] This compression device has the advantage that one or more single-stage compressors or discharge channels of a multi-stage compressor can switchably compress the refrigerant from a low pressure or a medium pressure to a higher pressure, while the remaining single-stage compressors or discharge channels of a multi-stage compressor can be connected in parallel to compress the refrigerant from the lower pressure to the higher pressure. This allows the compression device to be operated flexibly. It can be switched from compression with just one pressure difference to two compression stages connected in parallel with different pressure differences without the need for two-stage operation of compressors connected in series. There are no dedicated compressors or discharge channels for each compression stage, which advantageously saves space and material.All of the discharge channels or single-flow compressors of the compression device according to the invention can be operated in parallel to compress refrigerant from the lower pressure to the higher pressure, which is advantageous for the size of the volume flow to be compressed. Furthermore, when switching the compression device for operation with two different pressure differentials, the discharge channels or single-flow compressors are not connected in series, which advantageously prevents the total volume flow to be compressed from being significantly reduced. With a shuttle valve, no additional sensors are required; instead, switching is straightforward and immediate, depending on the pressure, without the valve having to be directly controlled for switching.For example, in a shuttle valve with automatic refrigerant flow at the inlet with a currently higher pressure and shutoff of the other inlet, which currently has a lower pressure, an additional pressure sensor is unnecessary. A compression device according to the invention with a switching device comprising one or more shuttle valves is therefore a simple, material-saving, and cost-effective design in which the shuttle valve(s) do not need to be directly controlled.

[0020] An advantageous embodiment of the compression device according to the invention comprises a multi-flow compressor, which is designed as a plunger compressor with multiple cylinders for the multiple discharge flows. In such a multi-flow compressor, the multiple discharge flows can be operated particularly well when connected in parallel to compress a refrigerant from a lower pressure to a higher pressure.

[0021] According to an advantageous development, one or more of the single-flow compressors or discharge flows of the multi-flow compressor are designed to be switchable. This makes the compression system particularly flexible. The volume flow of the refrigerant to be compressed can be adjusted as needed. This allows the performance of the compression system and thus energy consumption to be reduced as needed.

[0022] Preferably, a control system is designed such that it can control the switching on and off of the switchable single-flow compressor(s) or discharge flow(s). This enables automatic control of the volume flow rate of the refrigerant to be compressed.

[0023] The object with regard to a refrigerant circuit with an economizer is achieved by the features listed in claim 4. In that a refrigerant circuit comprises, on the high-pressure side, at least one condenser / gas cooler, the high-pressure side of an economizer, and a branch into a main branch and a secondary branch that can be switched off for the passage of refrigerant, wherein the secondary branch provided for the first partial flow of the refrigerant comprises a first expansion element and, in addition, the medium-pressure side of the economizer arranged downstream in the refrigerant flow direction, and the main branch provided for the second partial flow of the refrigerant, in the case of refrigerant flow division, comprises at least one second expansion element and, in addition, at least one evaporator arranged downstream in the refrigerant flow direction, wherein the refrigerant circuit comprises a compression device according to the invention for compressing the refrigerant,and a first suction gas inlet of the compression device is provided for the first partial flow of refrigerant coming through the secondary branch from the medium-pressure side of the economizer, and a second suction gas inlet of the compression device is provided for refrigerant coming through the main branch from the at least one evaporator, and the switching device of the compression device comprises a shuttle valve with an outlet to one or more of the switchable discharge flows or switchable single-flow compressors and with switching options of the shuttle valve for opening the valve passage for refrigerant from the first suction gas inlet or from the second suction gas inlet of the compression device, the problem is solved.

[0024] A gas cooler / condenser can be a condenser for refrigerant to be operated subcritically in the high-pressure area of the refrigerant circuit or a gas cooler for refrigerant to be operated supercritically in the high-pressure area of the refrigerant circuit, or it can be designed in such a way that it can be used both as a gas cooler and as a condenser.

[0025] With regard to the advantages as well as advantageous embodiments and further developments, the relevant above information on the compression device according to the invention applies accordingly. In particular, the shuttle valve automatically switches to allow refrigerant to pass through the suction gas inlet with a currently higher refrigerant pressure and to shut off the other suction gas inlet, which is currently at a lower pressure. An additional pressure sensor is unnecessary for this purpose. If the secondary branch preferably has a closable, controllable electronic expansion valve as the first expansion element, the switching device of the compression device can be switched automatically during operation of the refrigerant circuit by controlling the first expansion element alone. This means that both the expansion of the refrigerant and the shutting off and opening of the secondary branch can be controlled with just one valve.

[0026] Preferably, the secondary branch can be opened or closed to the passage of refrigerant, depending on whether the switching setting with or without an effective economizer is currently more economical. For this purpose, the compression setting can be easily adjusted using the compression device according to the invention, and in particular its switching device, without having to significantly change the volume flow of the refrigerant through the compression device.

[0027] According to an advantageous development, the first expansion element includes an MOP control. MOP stands for "maximum operating pressure." MOP control regulates an upper limit for the operating pressure, i.e., a maximum pressure of the refrigerant after expansion. This makes it easier to prevent excessively high evaporation temperatures of the refrigerant after flowing through the medium-pressure side of the economizer, which, for example, allows more flexibility in the dimensioning of the economizer.For example, in a thermostatic expansion valve with an MOP control, the filling quantity in the sensor is limited in such a way that from a certain evaporation temperature onwards the sensor filling is completely evaporated and thus the sensor pressure no longer increases significantly, which consequently changes the force ratio on the membrane in the expansion valve towards closing the expansion valve as the evaporation pressure continues to rise, thereby limiting the evaporation pressure to a maximum.

[0028] Preferably, the refrigerant circuit has a control system configured to control the first expansion element, taking into account any overheating of the refrigerant upstream of or at the first suction gas inlet of the compression device. With such a control system, the passage of refrigerant through the secondary branch can be automatically controlled and, for example, in a compression device according to the invention with a switching device comprising a shuttle valve, also its switching setting.

[0029] According to an advantageous embodiment, the control system is configured such that the first expansion element can be controlled taking into account the performance of the compression device and / or the temperature difference between the temperature of the heat sink at the at least one condenser / gas cooler and the temperature of the heat source at the at least one evaporator of the main branch. If the temperature difference is high enough for the economizer to improve the coefficient of performance, the control system can automatically open the passage for the first partial flow of refrigerant through the secondary branch, and set an average refrigerant pressure at the first suction gas inlet.

[0030] Preferably, the control system is configured such that, in the case of the first flow path(s) switched for the first partial flow of the medium-pressure refrigerant, the first expansion element and / or the second expansion element can be controlled while taking into account a control objective of harmonizing the power transferred from the crank mechanism to the refrigerant in the respective compression chambers. Particularly in a multi-flow plunger compressor, this reduces the risk of crankshaft imbalance, thereby minimizing disruptive compressor noise and reducing the susceptibility to damage and wear of the compression device.

[0031] According to an advantageous embodiment with a compression device having one or more switchable single-flow compressors or discharge channels of the multi-flow compressor, the control system is designed such that it can control the switching on and off of the switchable single-flow compressor(s) or discharge channels, taking into account the power requirement of the compression device for the refrigerant circuit. This allows the refrigerant circuit according to the invention to be operated particularly flexibly.

[0032] Preferably, the refrigerant circuit is intended for a heating and / or air conditioning system of a vehicle, such as a bus or rail vehicle in particular. The refrigerant circuit comprising an economizer and the flexibly operable, material- and space-saving compression device according to the invention is particularly well suited for this purpose.

[0033] The object with regard to a method for operating the refrigerant circuit is achieved by the features listed in claim 11. Due to the fact that the method for operating a refrigerant circuit according to the invention or a corresponding refrigerant circuit with a switching device provided for switching the switchable one or more conveying flows or single-flow compressors without a shuttle valve the steps of checking, taking into account the temperature difference between the temperature of the heat sink at at least one condenser / gas cooler and the temperature of the heat source at at least one evaporator of the main branch, whether the refrigerant circuit should be operated using the economiser, and, if the result of the previous test step is positive, the steps aa) opening or leaving open the secondary branch provided for the first partial flow of the refrigerant, so that the high-pressure side of the economiser is flowed through by refrigerant and the medium-pressure side of the economiser is flowed through by the refrigerant of the first partial flow, which has been expanded to a medium pressure in the first expansion element, and bb) switching or leaving switched over the one or more switchable conveying flows or switchable single-flow compressors in such a way,that they are operated to compress the refrigerant of the first partial flow from an average pressure lying between the lower pressure and the higher pressure to the higher pressure, with one or more of the remaining discharge flow(s) or one or more of the remaining single-flow compressor(s) being operated to compress the refrigerant of the second partial flow from the lower pressure to the higher pressure, or if the result of the test step is negative, the steps cc) closing or leaving closed the secondary branch provided for the first partial flow of the refrigerant so that only the high-pressure side of the refrigerant flows through the economiser, and dd) switching or leaving switched over the one or more switchable discharge flow(s) or switchable single-flow compressor(s) in such a way that they are operated to compress refrigerant coming from the main branch from a lower pressure to a higher pressure,The problem is solved by simultaneously operating one or more of the remaining delivery flow(s) or one or more of the remaining single-flow compressor(s) in parallel to compress refrigerant coming from the main branch from the lower pressure to the higher pressure.

[0034] An embodiment of the switching device without a shuttle valve can have one or more three-way switching valves controlled by the controller for switching, for example, instead of a shuttle valve for the method according to the invention.

[0035] One advantage is that the temperature difference between the heat sink temperatures at the condenser / gas cooler and the heat source at the evaporator can be taken into account when deciding whether to use the economizer. This temperature difference can be easily determined using temperature sensors and is an important criterion for deciding whether to use the economizer effectively in the refrigerant circuit.

[0036] According to an advantageous embodiment of the method, in a switching device comprising a shuttle valve with an outlet to one or more of the switchable discharge flows or single-flow compressors and with shuttle switching for opening the valve passage for refrigerant from the first suction gas inlet or from the second suction gas inlet of the compression device, the switching setting for step bb) is made by opening and the other switching setting for step dd) is made by closing the auxiliary branch. This is a simple way of switching the switchable single-flow compressors or switchable discharge flows of the multi-flow compressor without the need for additional sensors. In particular, an embodiment of the method is advantageous in which the first expansion element in the auxiliary branch is designed as a controllable electronic expansion valve and is or remains opened for step aa) and is or remains closed for step cc).Thus, for steps aa) with bb) and cc) with dd), only the first expansion element needs to be controlled, whereby the superheating of the refrigerant in or at the first suction gas inlet of the compression device is additionally controlled with the first expansion element.

[0037] Preferably, in the first step, the result of the test to determine whether the refrigerant circuit should be operated with the economizer depends on the economic efficiency of using the economizer. The secondary branch can be opened or closed to the passage of refrigerant, depending on whether the switching setting with or without an effective economizer is more economical. For this purpose, the compression setting can be easily adjusted using the compression device, and in particular its switching device, without having to significantly change the volume flow of the refrigerant through the compression device.

[0038] According to an advantageous development of the method, in the case of operation of the refrigerant circuit using the economizer for the control objective of harmonization in the respective compression chambers, the first expansion element is / are controlled by the crank operation of the multi-flow plunger compressor of a compression device designed in this way in such a way that the superheating of the refrigerant is selected in an operating point-optimized manner before or at the first suction gas inlet of the compression device.

[0039] This counteracts the risk of imbalance in the crankshaft of the compression device, which reduces noise, susceptibility to damage and wear of the compression device.

[0040] According to an advantageous embodiment, the method according to the invention for operating a refrigerant circuit with a compression device having one or more switchable single-flow compressors or discharge channels of a multi-flow compressor comprises the further steps of determining the power requirement of the compression device for the refrigerant circuit and switching one or more of the switchable single-flow compressors or discharge channels on or off depending on the determined power requirement. This utilizes further possible combinations of switching such a compression device. In this way, the refrigerant circuit is adapted particularly flexibly to the respective current demand. The refrigerant circuit is thus operated in an energy-saving manner at partial load. Short description of the drawings:

[0041] Embodiments of the invention are explained with reference to the drawings. It shows

[0042] Fig. 1a in schematic representation an embodiment of a compression device according to the invention with a multi-flow compressor in a switching setting of the switching device; Fig. 1b in schematic representation the Fig. 1a shown embodiment of a compression device according to the invention in the other switching setting of the switching device; Fig. 2a in schematic representation a further embodiment of a compression device according to the invention with a multi-flow compressor with a switchable conveying flow with switching setting of the switching device; Fig. 2b in schematic representation the Fig. 2a shown embodiment of a compression device according to the invention in the other switching setting of the switching devices; Fig. 3a in a schematic representation of an embodiment of a refrigerant circuit with a compression device according to the invention in a switching setting of the switching device; Fig. 3b in schematic representation the Fig. 3a shown embodiment of a refrigerant circuit with a compression device according to the invention in the other switching setting of the switching device; Fig. 4 in a schematic representation of an embodiment of a refrigerant circuit for operation with a method according to the invention; Fig. 5 as a flowchart an embodiment of a method according to the invention for operating a refrigerant circuit; and Fig. 6 as a flow chart a further embodiment of a method according to the invention for operating a refrigerant circuit. Detailed description of the invention:

[0043] All drawings are schematic. Scaled illustrations have been omitted for the sake of clarity.

[0044] In Figur 1a an embodiment of a compression device 1 according to the invention with a multi-flow compressor 3 in a switching setting of the switching device 5 is shown schematically.

[0045] The multi-flow compressor 3 has four discharge passages 9, 9a in the compressor housing 7, each with a cylinder 11. Designs of multi-flow compressors 3 with two, three, or more than four discharge passages 9, 9a are also possible. The multi-flow compressor 3 is designed as a plunger compressor. Other known suitable types of multi-flow compressors 3 are also conceivable.

[0046] The four delivery flutes 9, 9a are connected in parallel to compress a refrigerant from a lower pressure to a higher pressure. The outlets of the delivery flutes 9, 9a for refrigerant compressed to a higher pressure in the cylinders 11 are at the same pressure level and together open into a refrigerant line. One delivery flute 9a of the four delivery flutes 9, 9a is switchable such that, when switched, it can be operated to compress the refrigerant of a first partial flow from an intermediate pressure lying between the lower pressure and the higher pressure to the higher pressure, while simultaneously the remaining three delivery flutes 9 can be operated to compress the refrigerant of a second partial flow from the lower pressure to the higher pressure.

[0047] Variants of multi-flow compressors 3 are also possible, in which more than one discharge flow 9a is configured to be switchable in this way. The switching device 5 arranged outside the compressor housing 7 is provided for switching; in this case, it is designed as a shuttle valve.

[0048] As a possible alternative, the switching device 5 can be positioned in the compressor housing 7.

[0049] One inlet 13a of the switching device 5 is intended for refrigerant at the same pressure as the inlets of the three non-switchable discharge channels 9. Upstream of this in the intended refrigerant flow direction, the second suction gas inlet 15 of the compression device 1 is arranged as the low-pressure connection of the multi-flow compressor 3 for the inflow of low-pressure refrigerant. The other inlet 13b of the switching device 5 is intended as a medium-pressure connection, a first suction gas inlet of the compression device 1 for a first partial flow of medium-pressure refrigerant, i.e., not at the same pressure as the inlets of the three non-switchable discharge channels 9 intended for low-pressure refrigerant. The outlet of the switching device 5 leads to the switchable discharge channel 9a. The switching device 5, designed as a single shuttle valve, has two switching settings during operation in this case.In one switching setting, one inlet 13a is open and its other inlet 13b is closed; in the other switching setting, the situation is exactly the opposite. Thus, the one of the two inlets 13a, 13b of the switching device 5 is open at which the refrigerant pressure is higher than that at the other. The spherical closure body 17 in the switching device 5 closes the inlet 13a, 13b at which a lower pressure is present. Figur 1a In the switching device 5, the inlet 13a for the parallel connection of all four conveying flutes 9, 9a for compressing refrigerant from a lower pressure to a higher pressure is open, and the other inlet 13b is closed. In this case, the other inlet 13b would therefore not be at an average pressure during operation, but rather at a lower pressure than the low pressure of the refrigerant from the second suction gas inlet 15.

[0050] In Figur 1b is with the same reference numerals the one in Figur 1a The embodiment of a compression device 1 shown is shown in the other switching setting of the switching device 5. In the switching setting shown there, the inlet 13b of the switching device 5 is open as a medium-pressure connection, to which refrigerant at medium pressure is present during operation, and the other inlet 13a for refrigerant from the second suction gas inlet 15 is closed. Thus, the switchable conveying flues 9a for compressing refrigerant of a first partial flow at medium pressure is switched from the medium-pressure connection to a higher pressure. The three non-switchable conveying flues 9 for compressing refrigerant of a second partial flow at low pressure are switched from the second suction gas connection 15 to the higher pressure.

[0051] In Fig. 2a A further exemplary embodiment of a compression device 1 according to the invention with a multi-flow compressor 3 with a switchable delivery flow 9b is shown schematically in a switching setting of the switching device 5. The multi-flow compressor 3 has four delivery flows 9, 9a, 9b in the compressor housing 7, each with a cylinder 11. The multi-flow compressor 3 is designed as a plunger compressor. The four delivery flows 9, 9a, 9b are connected in parallel to compress a refrigerant from a lower pressure to a higher pressure. The outlets of the four delivery flows 9, 9a, 9b for refrigerant compressed to a higher pressure in the cylinders 11 are at the same pressure level and together open into a refrigerant line.Two conveying flutes 9a, 9b of the four conveying flutes 9, 9a, 9b are switchable in such a way that, when switched, they can be operated to compress the refrigerant of a first partial flow from a medium pressure lying between the lower pressure and the higher pressure to the higher pressure, while at the same time the remaining two conveying flutes 9 can be operated to compress the refrigerant of a second partial flow from the lower pressure to the higher pressure.

[0052] The switching device 5 located inside the compressor housing 7 is provided for switching purposes; in this case, it is designed as a single shuttle valve. As a possible alternative, the switching device 5 can be positioned outside the compressor housing 7.

[0053] One inlet 13a of the switching device 5 is intended for refrigerant at the same pressure as the inlets of the two non-switchable conveying flues 9. Upstream of this in the intended refrigerant flow direction is the second suction gas inlet 15 of the compression device 1, which functions as a low-pressure connection, for the inflow of low-pressure refrigerant. The other inlet 13b of the switching device 5 is provided immediately after the first suction gas inlet 37 for a first partial flow of medium-pressure refrigerant, i.e., not at the same pressure as the inlets of the two non-switchable conveying flues 9, which are intended for low-pressure refrigerant. The outlet of the switching device 5 leads to the two switchable conveying flues 9a, 9b. The switching device 5, designed as a shuttle valve, has two switching settings during operation in this case.The switching device 5 with its switching settings which can be switched by means of the spherical closing body 17 of the shuttle valve corresponds to that shown in . Figur 1a described. Thus, the one of the two inlets 13a, 13b of the switching device 5 is open at which the applied refrigerant pressure is higher than that at the other.

[0054] In Figur 2a In the switching device 5 designed as a shuttle valve, the inlet 13a for the parallel connection of all four conveying flues 9, 9a, 9b for refrigerant with a low pressure is opened by the second suction gas inlet 15, and the other inlet 13b of the switching device 5 is closed. However, one conveying flue 9b of the switchable conveying flues 9a, 9b is designed to be switchable. It can be switched on with the three other conveying flues 9, 9a connected in parallel to compress refrigerant with a low pressure to a higher pressure. Figur 2a however, it is shown switched off. The three-way valve 19 at the outlet of the switchable conveying flue 9b, which can be switched using the control 21, is switched to shut off the high-pressure area and to return refrigerant to the inlet of the switchable conveying flue 9b, so that a short-circuit line to the suction gas area of the thus switched off conveying flue 9b exists. The switching off of the conveying flue 9b is intended in particular for operation of the compression device 1 with reduced power, such as during partial load operation. The switchable conveying flue 9b is therefore switchable in two ways. It can be switched off and switched over.

[0055] Designs of multi-flow compressors 7 are conceivable in which more than one switchable delivery flow 9b of parallel-connectable delivery flows 9, 9a, 9b are arranged.

[0056] In Figur 2b is with the same reference numerals the one in Figur 2a shown embodiment of a compression device 1 in the other switching setting of the switching device 5. In the switching setting shown there, the inlet 13b of the switching device 5 is open as a medium-pressure connection, to which refrigerant at medium pressure is present during operation, and the other inlet 13a for refrigerant from the second suction gas inlet 15 is closed. Thus, the two switchable conveying channels 9a, 9b are switched for compressing refrigerant of a first partial flow at medium pressure from the first suction gas inlet to a higher pressure. The switchable conveying channel 9b is shown switched on. The three-way valve 19 at the outlet of the switchable conveying channel 9b, which can be switched using the control 21, is switched to open to the high-pressure region and to shut off the return of refrigerant to the inlet of the switchable conveying channel 9b.

[0057] Other known suitable types of shut-off flow channels are also conceivable, such as cylinder bank shut-off, in which a bypass is opened via a solenoid valve between two adjacent counter-rotating cylinders, with the first cylinder then pushing the gas volume into the second cylinder and vice versa. This creates a short-circuit connection of refrigerant between cylinders.

[0058] Furthermore, the two non-switchable conveying flows 9 for compressing refrigerant of a second partial flow with low pressure from the second suction gas inlet 15 are switched to the higher pressure.

[0059] In Figur 3a is a schematic illustration of an exemplary embodiment of a refrigerant circuit 23 with a compression device 1 according to the invention in a switching setting of the switching device 5. The refrigerant circuit 23 runs on the high-pressure side from the outlet of the compression device 1 to the condenser / gas cooler 25 and then to the high-pressure side of an economizer 27 and then to a branch 29. At the branch 29, the refrigerant line branches into a main branch 31 and a secondary branch 33. An alternative arrangement is also conceivable in which the branch 29 is located upstream of the high-pressure side of the economizer 27, which is then located in the main branch 31, in the direction of refrigerant flow. In the secondary branch 33, the refrigerant line leads to the first expansion element 35, which is designed as a closable, controllable electronic expansion valve.During operation, the refrigerant passage through the secondary branch 33 can be switched on and off by closing and opening the first expansion element 35. In the open first expansion element 35, the refrigerant of the first partial flow is expanded to a medium pressure. The medium-pressure side of the economizer 27 is arranged in the secondary branch 33 downstream of the first expansion element 35 in the refrigerant flow direction. The secondary branch 33 then leads to the first sag gas inlet 37 of the compression device 1, which in this case forms the medium-pressure connection of one inlet 13b of the switching device 5, designed as a shuttle valve.

[0060] From the branch 29, the main branch 31 leads to the second expansion element 39, which is designed to expand the refrigerant flowing through the main branch 29 during operation to a lower pressure. For this purpose, the evaporator 41 is arranged downstream in the refrigerant flow direction in the main branch 31. During operation, the refrigerant evaporated into suction gas from the evaporator 41 flows to the second suction gas inlet 15 of the compression device 1. The compression device 1 comprises a multi-flow compressor 3 designed as a plunger compressor with four cylinders 11 of the four discharge flows 9, 9a, 9b. The switching device 5 is located outside the compressor housing 7. The outlet of the switching device 5, which is designed as a single shuttle valve, leads into the one switchable conveying flow 9a of the multi-flow compressor 3. Of the remaining three non-switchable conveying flows 9, 9b, two are designed as switchable conveying flows 9b.For this purpose, a three-way valve 19 is located at each outlet, which, in the event of the respective switchable compressor flow 9b being switched off, would be switched to shut off the high-pressure area and to return refrigerant to the inlet of the respective switchable delivery flow 9b.

[0061] The four conveying flutes 9, 9a, 9b are connected in parallel to compress a refrigerant from a lower pressure to a higher pressure. The outlets leading from the four conveying flutes 9, 9a, 9b for refrigerant compressed to a higher pressure in the cylinders 11 are at the same pressure level for refrigerant and together open into the refrigerant line to the condenser / gas cooler 25. One switchable conveying flute 9a is switchable such that, when switched, it can be operated to compress the refrigerant of a first partial flow from an intermediate pressure lying between the lower pressure and the higher pressure to the higher pressure, while simultaneously the remaining three conveying flutes 9, 9b can be operated to compress the refrigerant of a second partial flow from the lower pressure to the higher pressure.

[0062] One inlet 13a of the switching device 5 is provided for refrigerant at the same pressure as the inlets of the three non-switchable conveying flows 9, 9b. Upstream of this in the intended refrigerant flow direction, the second suction gas inlet 15 is arranged as the low-pressure connection of the multi-flow compressor 3 for the inflow of low-pressure refrigerant. The other inlet 13b of the switching device 5 is provided as the first suction gas inlet 37 of the compression device 1 for a first partial flow of medium-pressure refrigerant. The closure body 17, designed as a sphere, in the switching device 5, designed as a shuttle valve, closes the inlet 13a, 13b at which a lower pressure is present. Figur 3a In the switching device 5 designed as a shuttle valve, the inlet 13a for the parallel connection of all currently not switched off conveying flows 9, 9a, 9b for compressing refrigerant from a lower pressure to a higher pressure is open and the other inlet 13b is closed. Due to the switched off secondary branch 33, the pressure at the other inlet 13b is lower than the lower pressure of the refrigerant coming from the main branch 31 through the second suction gas inlet 15. The controller 43 controls in the Figur 3a In the setting of the refrigerant circuit 23 shown, the two three-way valves 19 at the respective outlet of the two switchable conveying flues 9b are set to allow refrigerant to pass to the condenser / gas cooler 25 in the high-pressure area and to shut off the return of refrigerant to the inlet of the respective switchable conveying flues 9b. Furthermore, the control 43 controls the first expansion element 35 to close or shut off, so that the secondary branch 33 is switched off for refrigerant to flow through and thus, during operation, the undivided refrigerant flow flows through the main branch 31 to the second suction gas inlet 15.

[0063] Depending on the power requirement of the compression device 1 for the refrigerant circuit 23, one or both switchable discharge channels 9b can be switched off, with the control 43 switching the respective switchable three-way valve 19 at the outlet of the respective switchable discharge channels 9b to shut off the high-pressure area and to return refrigerant to the inlet of the switchable discharge channel 9b, so that a short-circuit connection to its suction gas area exists and it is thus switched off. Other known suitable types of switchable discharge channels are also conceivable, such as cylinder bank switch-off. For example, the use of the multi-flow compressor 3 with one or two switched-off discharge channels 9b is suitable for partial load operation of the refrigerant circuit 23.

[0064] In Figur 3b is with the same reference numerals the one in Figur 3a In the exemplary embodiment of a refrigerant circuit 23 shown, the compression device 1 is shown in the other switching setting of the switching device 5. In the switching setting shown there, the inlet 13b of the switching device 5 is open as the first suction gas inlet 37, to which, during operation, refrigerant of the first partial flow through the secondary branch 33 is present at medium pressure, and the other inlet 13a is closed for refrigerant from the second suction gas inlet 15. Thus, the switchable conveying flute 9a is switched to compress refrigerant of a first partial flow at medium pressure from the secondary branch 33 to a higher pressure. A refrigerant flow division takes place at the branch 29. For this purpose, the first expansion element 35 is controlled by the controller 43 for a corresponding expansion of the first partial flow of refrigerant flowing through the secondary branch 33.In this case, overheating of the refrigerant before the first suction gas inlet 37 of the compression device 1 is taken into account.

[0065] The first expansion device 35 has an MOP control to limit the maximum pressure upstream of the first suction gas inlet 37. Furthermore, the three non-switchable discharge flues 9, 9b for compressing refrigerant of the second partial flow through the main branch 31 with low pressure are switched from the second suction gas connection 15, which functions as a low-pressure connection, to the higher pressure. The economizer 27 is switched to operation. During operation, refrigerant flows through its high-pressure side and its medium-pressure side in a countercurrent arrangement. The dimensioning of the economizer with its heat transfer surface is adapted to the displacement ratio of the switchable discharge flues 9a to the three non-switchable discharge flues 9, 9b, as well as to the greatest temperature difference between the heat source at the evaporator 41 and the heat sink at the condenser / gas cooler 25.The controller 43 controls the first expansion element 35 taking into account the temperature difference between the temperature of the heat sink on at least one condenser / gas cooler 25 and the temperature of the heat source on at least one evaporator 41 of the main branch 31. If the temperature difference is high, the controller 43 must . Figur 3b shown setting and with a small temperature difference the setting in Figur 3a shown setting.

[0066] The refrigerant circuit 23 is intended for a heating and / or air conditioning system of a vehicle, such as a bus or rail vehicle.

[0067] In this case, the refrigerant circuit 23 is designed to be pressure-resistant for supercritical refrigerant operation in the high-pressure range. The refrigerant in this case is CO2.

[0068] A variant is conceivable in which the refrigerant circuit 23 is designed to be operated subcritically, for example with the refrigerant R1234yf.

[0069] In Figur 4 An embodiment of a refrigerant circuit 23 for operation with a method according to the invention is shown schematically.

[0070] On the high-pressure side, the compressed refrigerant is led from the outlet of the compression device 1 through the condenser / compressor 25 to the branch 29 in the main branch 31 and the secondary branch 33, which can be switched off for the refrigerant passage. The main branch 31 contains the high-pressure side of the economizer 27 and then the second expansion element 39, which is designed as an electronic expansion valve controllable by the controller 43. Downstream of the second expansion element 39 in the refrigerant flow direction is the evaporator 41 for evaporating refrigerant, which then flows as suction gas to the second suction gas inlet 15 of the compression device 1 during operation at low pressure. In the secondary branch 33, upstream of the medium-pressure side of the economizer 27 in the refrigerant flow direction, the first expansion element 35, designed as a closable, controllable electronic expansion valve, is arranged.In the secondary branch 33, downstream of the medium-pressure side of the economizer 27, is the first suction gas inlet 37 of the compression device 1, which is intended for suction gas at medium pressure and is also one inlet 13b of the switching device 5. The switching device 5 comprises a three-way switching valve switchable by the controller 43, which distinguishes it from a compression device according to the invention. The second inlet 13a thereof is intended for refrigerant from the second suction gas inlet 15. The compression device 1 has three single-flow compressors 47, 47a, which are configured such that they can be operated in parallel to compress a refrigerant from a lower pressure to a higher pressure.Of these, a single-flow compressor 47a is switchably arranged at the outlet of the switching device 5 such that, when the three-way switching valve of the switching device 5 is switched, it can be operated to compress the refrigerant of the first partial flow flowing through the opened secondary branch 33 from an average pressure lying between the lower pressure and the higher pressure to the higher pressure, wherein at the same time the remaining two single-flow compressors 47 can be operated to compress the refrigerant of the second partial flow flowing through the main branch 31 from the lower pressure to the higher pressure.The controller 43 controls the respective switching setting for passing low-pressure refrigerant from the second suction gas inlet 15 or medium-pressure refrigerant from the first suction gas inlet 37 to the switchable single-flow compressor 47a by appropriately switching the three-way switching valve of the switching device 5 and the first expansion element 35.

[0071] The controller 43 controls the first expansion element 33, the switching device 5, the second expansion element 39 and the output of the single-flow compressors 47, 47a, taking into account an overheating of the refrigerant at the first suction gas inlet 37 of the compression device 1 and the temperature difference between the temperature of the heat sink at the condenser / gas cooler 25 and the temperature of the heat source at at least one evaporator 41 of the main branch 31.

[0072] In Figur 5 is a flowchart illustrating an embodiment of a method for operating a Figur 4 shown refrigerant circuit or a refrigerant circuit according to the invention, such as one shown in the Figuren 3a and 3b shown.

[0073] In the first step 100, measurement data such as in particular the temperatures of the heat sink at the condenser / compressor and the heat source at the evaporator of the refrigerant circuit are received by the controller.

[0074] In the first step 110, the received measurement data is used to determine whether or not the refrigerant circuit should be operated using the economizer. This check takes into account the temperature difference between the temperature of the heat sink at at least one condenser / gas cooler and the temperature of the heat source at at least one evaporator of the main branch, with the decision depending in particular on the economic viability of using the economizer. If a large temperature difference is detected between the heat source and the heat sink, the use of an economizer is more economical than in the case of a small temperature difference.

[0075] If the result of the decision 120 based on the test in step 110 is positive, i.e. "yes", for the use of the economizer, the secondary branch for the passage for the first partial flow of the refrigerant is opened or left open in the following step 130, so that the high-pressure side of the economizer is flowed through by refrigerant and the medium-pressure side of the economizer is flowed through by the refrigerant of the first partial flow, which has been expanded to a medium pressure in the first expansion element.

[0076] In step 140, which usually takes place simultaneously with step 130, one or more of the switchable conveying flows or single-flow compressors is / are switched or left switched in such a way that it is operated to compress the refrigerant of the first partial flow coming from the secondary branch from an average pressure of, for example, 40 bar, lying between the lower pressure of, for example, 20 bar and the higher pressure of, for example, 100 bar, to the higher pressure, wherein at the same time one or more of the remaining conveying flows or one or more of the remaining single-flow compressors is / are operated to compress the refrigerant of the second partial flow coming from the main branch from the lower pressure to the higher pressure.

[0077] However, if the result of the decision 120 based on the test in step 110 is against the use of the economizer, i.e. negative as "no", in the following step 130a the secondary branch provided for the first partial flow of the refrigerant is closed or left closed, so that only the high-pressure side of the economizer is flowed through by refrigerant.

[0078] In step 140a, which usually takes place simultaneously with step 130a, one or more of the switchable conveying flows or switchable single-flow compressors is / are switched or left switched in such a way that it is operated to compress refrigerant coming from the main branch from a lower pressure of, for example, 30 bar to a higher pressure of, for example, 90 bar, wherein in parallel thereto, one or more of the remaining conveying flows or one or more of the remaining single-flow compressors of the compression device is / are also operated to compress refrigerant coming from the main branch from the lower pressure to the higher pressure.

[0079] After a predetermined period of time, for example one second, the method begins again starting with step 100 after steps 140 or 140a.

[0080] The test in step 110 is carried out automatically in the control of the refrigerant circuit, whereby received measurement data transmitted to the control from temperature sensors for measuring the temperatures of the heat source at the evaporator and the heat sink at the condenser / gas cooler as well as the refrigerant at the first and second suction gas inlet of the compression device are processed.

[0081] The first expansion element is designed as a controllable electronic expansion valve, which is opened or remains open for the execution of step 130 and is closed or remains closed for the execution of step 130a.

[0082] When carrying out the method for operating, for example, a Figuren 3a and 3bIn the case of the refrigerant circuit shown with a switching device comprising a shuttle valve with an outlet to one or more of the switchable conveying flows or single-flow compressors and with shuttle switching for opening the valve passage for refrigerant from the first suction gas inlet or from the second suction gas inlet of the compression device, the switching settings for step 140 are made automatically by opening the secondary branch for the refrigerant passage and the other switching setting for step 140a is made automatically by closing the secondary branch. The shuttle valve switches automatically according to the respective sign of the pressure difference of the refrigerant between the first and second suction gas inlets. In the case of a switching device comprising a shuttle valve, steps 130 and 140 therefore strictly speaking take place in one step. The same applies to steps 130a and 140a.

[0083] In Figur 6 is a flow chart of a further embodiment of a method for operating a refrigerant circuit according to the invention, such as the one shown in Figuren 3a and 3b shown. The compression device has a multi-flow compressor designed as a plunger compressor with several cylinders, wherein at least one delivery flow is switchable and two delivery flow is switchable.

[0084] In the first step 200, the controller receives measurement data such as temperatures transmitted by temperature sensors of the heat sink on the condenser / gas cooler, the heat source on the evaporator of the refrigerant circuit and the refrigerant at the first and second suction gas inlet of the compression device, as well as from an acoustic sensor on the compression device.

[0085] In the following step 210, the power requirement of the compression device for the refrigerant circuit is determined using the received measurement data. Based on the determined power requirement, in step 220 one or more of the switchable discharge channels are switched off or on, or left switched off or on, depending on the determined power requirement. For example, the power requirement for partial load operation of the refrigerant circuit is rather low, so one or even both of the switchable discharge channels are switched off.

[0086] The next steps of checking 230 the use of the economizer and deciding 240 whether to open 250 or close 250a the secondary branch and switching 260 the switchable discharge flow for medium pressure refrigerant from the secondary branch or switching 260a the switchable discharge flow for low pressure refrigerant from the main branch are carried out as described in the Figur 5 described steps 110, 120, 130, 130a, 140 and 140a. In this case, the switching of steps 260 and 260a takes place automatically with the opening 250 or closing 250a of the secondary branch, because the switching device is designed as a shuttle valve, so that the inlet to which the higher pressure is applied is always automatically opened and the other inlet is closed.

[0087] In addition, the further steps 270 and 280 are carried out in Figur 6 shown method after the step of switching 260 the switchable conveying flutes for the first partial flow of the refrigerant coming from the secondary branch with medium pressure, wherein at the same time one or more of the remaining conveying flutes that are not switched off are operated to compress the refrigerant of the second partial flow coming from the main branch from the lower pressure to the higher pressure.

[0088] In step 270, the optimal operating point is determined for the control objective of harmonizing the crank operation of the multi-flow plunger compressor in the respective compression chambers using the measurement data received by the controller in step 200. Particular consideration is given to the aspect of minimizing noise emissions from the compression device. Due to the asymmetric loading of the multi-flow compressor's crankshaft, the operating conditions have changed. As a result, the multi-flow compressor will likely emit increased noise and vibration to the outside. The optimal operating point, particularly for reducing the cylinder load asymmetry to a tolerable level, requires a refrigerant superheat that is not necessarily thermodynamically optimal before or at the first suction gas inlet.

[0089] In the following step 280, the first expansion element is controlled in such a way that the superheating of the refrigerant before or at the first suction gas inlet of the compression device is selected to be optimal for the operating point.

[0090] After a predetermined period of time, for example two seconds, the method begins again starting with step 200 after steps 280 or 260a.

Claims

1. Compression device (1) comprising a plurality of single-flow compressors (47, 47a) or a multi-flow compressor (3) with a plurality of delivery flows (9, 9a, 9b), wherein the delivery flows (9, 9a, 9b) or the single-flow compressors (47, 47a) are configured in such a way that they are operable in parallel to compress a refrigerant from a lower pressure to a higher pressure, wherein one or more of the plurality of delivery flows (9, 9a, 9b) or single-flow compressors (47, 47a) are configured to be switchable in such a way that, in a switching setting, it / they are operable to compress the refrigerant of a first partial flow from a medium pressure lying between the lower pressure and the higher pressure to the higher pressure, wherein at the same time the remaining one / the other of the plurality of delivery flows (9, 9a, 9b) or single-flow compressors (47, 47a) is / are operable to compress the refrigerant of a second partial flow from the lower pressure to the higher pressure,characterized in that the compression device (1) has at least one switching device (5) arranged in such a way that it comprises one or more shuttle valves and is provided for switching the switchable one or more conveying flows (9, 9a, 9b) or single-flow compressor (47, 47a).

2. Compaction device (1) according to claim 1 characterized in that the multi-flow compressor (3) is designed as a plunger compressor with several cylinders (11) for the several delivery flows (9, 9a, 9b).

3. Compaction device (1) according to claim 1 or 2 characterized in that one or more of the single-flow compressors (47, 47a) or conveying flows (9, 9a, 9b) of the multi-flow compressor (3) are designed to be switchable off.

4. Refrigerant circuit (23) comprising, on the high-pressure side, at least one condenser / gas cooler (25), the high-pressure side of an economizer (27), and a branch (29) into a main branch (31) and a secondary branch (33) that can be switched off for the passage of refrigerant, wherein the secondary branch (33) provided for the first partial flow of the refrigerant comprises a first expansion element (35) and, in addition, the medium-pressure side of the economizer (27) arranged downstream in the refrigerant flow direction, and the main branch (31) provided for the second partial flow of the refrigerant in the case of refrigerant flow division comprises at least one second expansion element (39) and, in addition, at least one evaporator (41) arranged downstream in the refrigerant flow direction, characterized in thatthe refrigerant circuit (23) for compressing the refrigerant comprises a compression device (1) according to one of claims 1 to 3, wherein a first suction gas inlet (37) of the compression device (1) is provided for the first partial flow of the refrigerant coming through the secondary branch (33) from the medium-pressure side of the economizer (27), and a second suction gas inlet (15) of the compression device (1) is provided for refrigerant coming through the main branch (31) from the at least one evaporator (41), and the switching device (5) of the compression device (1) comprises a shuttle valve with an outlet to one or more of the switchable conveying flows (9, 9a, 9b) or switchable single-flow compressors (47, 47a) and with switching options of the shuttle valve for opening the valve passage for refrigerant from the first suction gas inlet (37) or from the second suction gas inlet (15) of the compression device (1) includes.

5. Refrigerant circuit (23) according to claim 4 characterized in that the first expansion element (35) is designed as a controllable electronic expansion valve which can be closed.

6. Refrigerant circuit (23) according to claim 4 or 5 characterized in that the first expansion element (35) comprises an MOP control.

7. Refrigerant circuit (23) according to one of claims 4 to 6 characterized in that it has a control system (43) designed in such a way that the first expansion element (35) can be controlled taking into account an overheating of the refrigerant before or at the first suction gas inlet (37) of the compression device (1).

8. Refrigerant circuit (23) according to one of claims 4 to 7 characterized in thatthe control (43) is designed such that the first expansion element (35) can be controlled taking into account the performance of the compression device (1) and / or the temperature difference between the temperature of a heat sink on the at least one condenser / gas cooler (25) and the temperature of a heat source on the at least one evaporator (41) of the main branch.

9. Refrigerant circuit (23) according to one of claims 4 to 8 with a compression device (1) according to claim 2 characterized in that the control (43) is designed such that, in the case of conveying flow(s) (9, 9a, 9b) switched over for the first partial flow of the refrigerant with medium pressure, the first expansion element (35) and / or the second expansion element (39) can be controlled taking into account a control objective of harmonizing the power transferred from the crank mechanism to the refrigerant in the respective compression chambers.

10. Refrigerant circuit (23) according to one of claims 4 to 9 characterized in that it is intended for a heating and / or air conditioning system of a vehicle, such as in particular a bus or rail vehicle.

11. A method for operating a refrigerant circuit (23) according to one of claims 4 to 10, wherein, however, the switching device (5) provided for switching the switchable one or more conveying flows (9, 9a, 9b) or single-flow compressor (47, 47a) is not limited to one having one or more shuttle valves, characterized bythe steps a) of checking (110, 230), taking into account the temperature difference between the temperature of the heat sink at at least one condenser / gas cooler (25) and the temperature of the heat source at at least one evaporator (41) of the main branch (31), whether the operation of the refrigerant circuit (23) should take place using the economiser (27), b) if the result of step a) is positive, the steps aa) opening or leaving open (130, 250) the secondary branch (33) provided for the first partial flow of the refrigerant, so that the high-pressure side of the economiser (27) is flowed through by refrigerant and the medium-pressure side of the economiser (27) is flowed through by the refrigerant of the first partial flow, which has been expanded to a medium pressure in the first expansion element (35), and bb) switching or leaving switched (140, 260) the one or more switchable conveying flows (9, 9a, 9b) or switchable single-flow compressor (47, 47a) in such a way,that they are operated to compress the refrigerant of the first partial flow from an average pressure lying between the lower pressure and the higher pressure to the higher pressure, wherein at the same time one or more of the remaining delivery flow(s) (9, 9a, 9b) or one or more of the remaining single-flow compressor(s) (47, 47a) is / are operated to compress the refrigerant of the second partial flow from the lower pressure to the higher pressure, or c) if the result of step a) is negative, the steps cc) close or leave closed (130a, 250a) the secondary branch (33) provided for the first partial flow of the refrigerant, so that only the high-pressure side of the economizer (27) is flowed through by refrigerant, and dd) switch or leave switched (140a, 260a) the one or more switchable delivery flow(s) (9, 9a, 9b) or switchable single-flow compressor(s) (47, 47a) in such a way,that they are operated to compress refrigerant coming from the main branch (31) from a lower pressure to a higher pressure, wherein in parallel connection one or more of the remaining conveying flow(s) (9, 9a, 9b) or one or more of the remaining single-flow compressor(s) (47, 47a) is / are also operated to compress refrigerant coming from the main branch (31) from the lower pressure to the higher pressure.

12. Method according to one of claims 11, characterized in thatin a switching device (5) which comprises a shuttle valve with an outlet to one or more of the switchable conveying flows (9, 9a, 9b) or single-flow compressors (47, 47a) and with shuttle switching for opening the valve passage for refrigerant from the first suction gas inlet (37) or from the second suction gas inlet (15) of the compression device (1), the switching setting for step bb) is carried out by opening and the other switching setting for step dd) is carried out by closing the secondary branch (33).

13. Method according to claim 11 or 12 characterized in that in step a) the result of the check (110, 230) as to whether the refrigerant circuit (23) should be operated using the economiser (27) depends on the economic efficiency of using the economiser (27).

14. Method according to one of claims 11 to 13 characterized by thatin the case of a compression device (1) designed as a plunger piston compressor with a plurality of cylinders (11) for the plurality of delivery flows (9, 9a, 9b), for the control objective of harmonisation in the respective compression chambers from the crank operation of the multi-flow plunger piston compressor in the case of step b), the first expansion element (35) is controlled in such a way that the superheating of the refrigerant before or at the first suction gas inlet (37) of the compression device (1) is selected to be optimal for the operating point.

15. Method according to one of claims 11 to 14 for operating a refrigerant circuit (23) with the compression device (1), in which one or more of the single-flow compressors (47, 47a) or conveying flows (9, 9a, 9b) of the multi-flow compressor (3) are designed to be switchable off, characterized bythe further steps - of determining (270) the power requirement of the compression device (1) for the refrigerant circuit (23), - of switching off or switching on or leaving switched off or switched on (280) one or more of the switchable single-flow compressor(s) (47, 47a) or delivery flow(s) (9, 9a, 9b) depending on the determined power requirement.

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